• The Blade Method 9Ransburg’s No. 1 process),
- a straight sharp edge is used charged to about 90 KV
- the paint is slowly pumped onto the blade, it spreads out, and by the time it reaches the tip it comes off as small charged droplets.
- the shape of the workhead encourages a linear dispersion pattern
- least cost effective and flexible
• The Bell Method (Ransburg’s No. 2 process)
- uses a rotating bell or funnel to disperse the paint
- the bell head is about 1 ft. from the workpiece
- a potential of 90-100 KV is applied to the head while the work is grounded
- the head rotates at 900 r.p.m. to cause good paint dispersion
- good coverage for rounded surfaces
- better efficiency than blade method
- suited to spherical irregular shapes
- extra power/equipment to run motor
• ASIDE: the edge effect in electrostatic phenomenon leads to higher concentration of charges at corners and edges.
• The Disk Method (also Ransburg’s No. 2 process)
- similar to Bell method except that a flat disk is used.
- the geometry of the disk allows a much wider spray coverage
- advantages (compared to bell),
- well suited to irregular and long parts
- can be used for manual/movable spraying
- is well insulated to prevent shocks
- well suited to complex shape because of operator aiming
- most effecient and cost effective method
• Consider the comparative tables [source unknown],
• Air/Hydraulic Electrostatic Spraying
- large negatively charged (100KV) electrodes are placed at the side of a spray paint line
- work on the central conveyor is rounded,and uncharged paint is sprayed in.
- the sprayed paint enters the electic field, becomes negatively charged and is drawn to the work.
- can be upgraded to a full electrostatic method easily
- a higher paint wastage results.
- a typical spray gun head is modified to deposit a high voltage charge on the paint particles
- the paint is sprayed with a negative charge, and it is attracted to a grounded workpiece
- the paint is charged before passing through the spray head
• Control systems (power supplies) for spraying a resistive/non-resistive. Resistive systems use resistors to limit the maximum current that can be drawn, thus protecting the users. Non-resistive sysems require added safety precautions and are best suited to automate systems.
• The edge phenomenon can result in uneven distribution of paint near edges and corners.
• The Faraday cage effect will result in recessed areas that get less paint coverage.
• Safety issues include electrical shocks, ventillation (most paints are solvent based), and arcs from poor grounding or unexpected metal contact.
- part recognition on a conveyor
- booths are costly, but provide safety and process advantages